The present invention relates to the control of an operating mode of a radio communication device. More particularly the invention relates to a method and apparatus for operating an uplink in a multi-mode radio communication device.
New digital cellular communication systems, such as the Wideband Code Division Multiple Access (WCDMA) extension of the Global System for Mobile Communication (GSM) and Digital Cellular System (DCS) can utilize different operating modes for the transfer of digital information. For example, digital information can be transferred using two different duplex modes, Frequency Division Duplex (FDD) and Time Division Duplex (TDD), as are known in the art, and use different operating frequency bands. The GSM system operates in the 900, 1800 and 1900 MHz bands, while the DCS system also operates in the 1800 MHz band. Allowing the operation in the different FDD and TDD modes provides more efficient spectrum utilization. In addition, a communication can share CDMA and Time Division Multiple Access (TDMA) aspects.
Multi-mode communication devices are designed to transmit and receive digital communications using operating systems chosen from a plurality of multiple access techniques including TDMA, CDMA, GSM, and DCS, and will combine some of these techniques and incorporate them into one device. The receiver portion of a dual mode communication device for example, is similar to those which are not dual mode but are adapted to receive a combination of signals in accordance with any of the systems above. For example, a device operating in a FDD mode can be transmitting in an uplink (UL) on one operating system and receiving on a downlink (DL) on another operating system. In addition, the device is required to occasionally monitor various channel frequencies (FDD, TDD, GSM) of these systems to look for control channels of new base stations.
In order to provide time for a device to monitor for other cells, upper layer commands can direct the device to operate in a compressed mode. In compressed mode, the slot format is changed so as to provide a transmission gap leaving a open time period for the device to perform interfrequency power measurement, acquisition of a control channel of another base station, and handover, for example. When in compressed mode, the information normally transmitted during a frame is compressed in time in order to maintain the amount of data transferred within a frame.
One method to alleviate data throughput problems associated with utilizing a compressed mode is to have a second xe2x80x9cmonitoringxe2x80x9d receiver in the communication device, as outlined in the proposed standard xe2x80x9c3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical layerxe2x80x94Measurements (FDD) (Release 1999), V3.3.0, Sec. 6.1.1.1 (2000-06). The use of a second receiver eliminates the requirement for the communication device to use a compressed mode in the downlink. However, it may be a requirement for the device to use a compressed uplink mode. For example, a device can be transmitting on the uplink while monitoring the downlink using the second monitoring receiver. Unfortunately, in those cases where the monitoring frequency is close to the uplink transmission frequency (i.e., frequencies in the TDD or GSM/DCS 1800/1900 MHz bands), the communication device can actually interfere with itself. In other words, the transmit power of the device is picked up by, and interferes with, the receiver of the device. Therefore, it has been a requirement to use a compressed mode in the uplink to allow non-transmission time for the device to accurately monitor for base station control channels on nearby frequencies without transmitter interference. This is true even if there is little actual self-interference in the device.
In practice, typical receiver circuitry in a communication device comprises two general portions: a front end portion and a back end portion. The front end portion functions to perform initial filtering, amplification of the desired bandwidth, and conversion to an intermediate frequency for further processing by the backend portion of the receiver. The backend portion converts the signal to the baseband in preparation for digital signal processing. RF signals enter the front end portion via the antenna and are transferred from the front end to the back end.
Controlling the incoming signal power of a radio frequency receiver is essential to maintain signal levels within the operating range of the baseband circuitry and provide proper operation of the receiver. Out-of-band signal power degrades receiver performance as a result of the decreasing signal to noise ratio and receiver selectivity. This may occur when interfering adjacent signals are very strong compared to the desired on-channel signal, such as when a device is transmitting on the uplink while monitoring on a downlink at a nearby frequency. This results in the desired on-channel signal becoming desensitized due to out-of-band noise. Therefore, it is necessary to limit the received signal power prior to the baseband circuitry and maintain signal levels within the back end circuit""s operating range. Filter portions of the baseband circuitry reduce the adjacent interference noise signals by allowing only the desired on-channel frequency to pass through. However, the incoming aggregate power level prior to the baseband circuitry comprises the desired monitored signal as well as the interfering uplink energy. The prior art solution is to use uplink compressed or slotted mode whenever monitoring frequencies that are close to the uplink transmission frequency. However, this results in reduced data throughput as outlined above.
Therefore, there is a need to reduce the use of uplink compressed mode during receiver monitoring to increase data throughput. It would also be of benefit to determine those cases where transmitting and receiver at the same time do not result in significant self-interference in the communication device. It would also be advantageous to provide these improvement without any additional hardware or cost in the communication device.